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United States Patent |
6,206,663
|
Frenken
|
March 27, 2001
|
Piston pump
Abstract
The invention relates to a piston pump (1) for delivering a fluid at low
pressure and at a higher pressure, a higher delivery volume being provided
in one pumping cycle at low pressure than at a higher pressure, having a
low-pressure delivery piston (4), which is moved inside a pump cylinder
(2) and acts upon a pressure chamber (7) under prestress into its delivery
end position, a high-pressure delivery piston (11), an inlet valve (9) and
an outlet valve (9, 10), a fluid delivery path (5) furthermore being
provided between the inlet valve (9) and the outlet valve (10), and the
low-pressure delivery piston (4) being able to be moved back counter to
its prestress into a delivery starting position, and proposes, to achieve
effective delivery at low pressure and at a higher pressure with the
simplest possible construction, that the fluid delivery path (5) passes
through the low-pressure delivery piston (4), that a valve (6) is provided
in the low-pressure delivery piston (4), which valve shuts in the case of
movement into the delivery starting position, that the high-pressure
delivery piston (11) and the low-pressure delivery piston (4) operate in a
common pressure chamber (7), and that the high-pressure delivery piston
(11) moves the low-pressure delivery piston (4) counter to its prestress.
Inventors:
|
Frenken; Egbert (Wermelskirchen, DE)
|
Assignee:
|
Gustav Klauke GmbH (DE)
|
Appl. No.:
|
269093 |
Filed:
|
March 18, 1999 |
PCT Filed:
|
April 25, 1998
|
PCT NO:
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PCT/EP98/02474
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371 Date:
|
March 18, 1999
|
102(e) Date:
|
March 18, 1999
|
PCT PUB.NO.:
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WO99/04165 |
PCT PUB. Date:
|
January 28, 1999 |
Foreign Application Priority Data
| Jul 19, 1997[DE] | 197 31 054 |
| Oct 02, 1997[DE] | 197 43 747 |
Current U.S. Class: |
417/549; 417/262; 417/545 |
Intern'l Class: |
F04B 39//10; .53/12 |
Field of Search: |
417/549,260,262,267,545,555.1
|
References Cited
U.S. Patent Documents
2510150 | Jun., 1950 | Stephans | 417/250.
|
2820415 | Jan., 1958 | Born | 417/287.
|
2938465 | May., 1960 | McFarland | 417/252.
|
3016838 | Jan., 1962 | Bessiere | 417/206.
|
5575627 | Nov., 1996 | Vairin et al. | 417/252.
|
Primary Examiner: Walberg; Teresa
Assistant Examiner: Campbell; Thor
Attorney, Agent or Firm: Trexler, Bushnell, Giangiorgi, Blackstone & Marr, Ltd.
Claims
What is claimed is:
1. A piston pump for delivering a fluid at low pressure and at a higher
pressure, a higher delivery volume being provided in one pumping cycle at
low pressure than at a high pressure, said piston pump comprising:
a low-pressure delivery piston, which is moved inside a pump cylinder and
acts upon a pressure chamber under prestress into a delivery end position;
a high-pressure delivery piston;
an inlet valve and an outlet valve;
a fluid delivery path provided between the inlet valve and the outlet
valve; and
the low-pressure delivery piston being able to be moved back counter to its
prestress into a delivery starting position, characterized in that the
fluid delivery path passes through the low-pressure delivery piston, that
a valve is provided in the low-pressure delivery piston, which valve shuts
in the case of movement into the delivery starting position, in that the
high-pressure delivery piston and the low-pressure delivery piston operate
in a common pressure chamber, and in that the high-pressure delivery
piston moves the low-pressure delivery piston counter to its prestress.
2. A piston pump according to claim 1, wherein the high pressure delivery
piston has a smaller cross-section than a cross-section of the low
pressure delivery piston.
3. A piston pump according to claim 1, wherein the high-pressure delivery
piston moves the low-pressure delivery piston counter to its prestress.
4. A piston pump according to claim 1, wherein the valve is a
pressure-actuated non-return valve.
5. A piston pump according to claim 1, wherein the valve is a controlled
valve.
6. A piston pump according to claim 1, wherein the high-pressure delivery
piston actuates the valve.
7. A piston pump according to claim 1, wherein the valve is configured as a
plate valve.
8. A piston pump according to claim 1, wherein the valve has an actuating
end which passes through a piston head of the low-pressure delivery
piston.
9. A piston pump according to claim 1, wherein the prestress is achieved by
means of a spring.
10. A piston pump according to claim 1, wherein the spring prestresses the
valve into a closure position.
11. A piston pump according to claim 1, wherein the low-pressure delivery
piston has a stem-like projection at the rear end to reduce the fluid flow
path between the inlet valve and the low-pressure delivery piston.
12. A piston pump according to claim 1, wherein the pump cylinder has a
pump cylinder base which can be opened in service.
13. A piston pump according to claim 12, wherein the pump cylinder base is
secured by a screw connection in a pump housing.
14. A piston pump according to claim 12, wherein the pump cylinder base is
configured in a cup-like manner with a screwing-in thread on an outer wall
of the cup edge.
Description
The invention relates to a piston pump for delivering a fluid at low
pressure and at a higher pressure, a higher delivery volume being provided
in one pumping cycle at low pressure than at a higher pressure, having a
low-pressure delivery piston, which is moved inside a pump cylinder and
acts upon a pressure chamber under prestress into its delivery end
position, a high-pressure delivery piston, and an inlet valve and an
outlet valve, a fluid delivery path furthermore being provided between the
inlet valve and the outlet valve, and the low-pressure delivery piston
being able to be moved back counter to its prestress into a delivery
starting position.
Piston pumps of this type are used, for example, in manually operated or
motor-driven hand tools. In this context, reference is made to prior art,
for example, in accordance with U.S. Pat. Nos. 432,107, 5,195,354 and
2,688,231. This prior art relates to motor-driven hand tools for
compressing cable terminals or cable connectors. Furthermore, however, the
subject-matter of the invention is also important, for example, with
regard to shears, for example cable shears. In this context, reference is
made to the German Utility Model 94 16 535 and the German Patent
Application 196 49 932 which is not a prior publication. Moreover, pumps
of this type are also used in other areas of technology. Reference is
made, for example, to U.S. Pat. Nos. 2,845,033 and 674,381.
Pumps which have two pressure stages are frequently used, primarily for the
drive of hydraulic tools. Such pumps supply a far greater volume of oil up
to a certain limit pressure, which may be 5% of the maximum pressure, than
at maximum pressure. The operating speed of hydraulic devices can thus be
increased substantially because, in many tools, such as for example
compression tools for the compression of cable terminals, a certain idle
stroke must first be travelled before the workpiece is contacted and the
actual operation takes place with a high power requirement. During the
idle stroke, only the force of the piston restoring spring of the
hydraulic cylinder of the tool generally has to be bridged. A low oil
pressure is sufficient for this purpose.
Many different construction types of two-stage pumps are known. It is
possible, for example, to combine two different pump construction types
with one another and drive them at the same time, that is to say, for
example, a gear pump for the low pressure range and a piston pump for the
high pressure range. As soon as the required starting pressure exceeds the
operating pressure of the low-pressure pump, its delivery flow is fed back
into the tank via a pressure relief valve.
Two-stage piston pumps are particularly common for manually actuated
hydraulic tools, where partial piston pumps are used both for the low
pressure and for the high pressure. A widespread construction is one in
which both pistons are combined in the form of a pump plunger with two
different diameters. The hydraulically active surface in the low-pressure
part is the annular surface between the two diameters and, in the
high-pressure piston, it is the entire cross-sectional area of the small
diameter. Both the low-pressure and the high-pressure pump each have an
inlet valve connected to the tank and an outlet valve connected to the
delivery side. A pressure relief valve is required additionally for the
low-pressure stage, by means of which valve the oil flows back into the
tank when the pressure of the low-pressure stage has been exceeded.
U.S. Pat. No. 4,492,106 relates to a lever-actuated hand tool in a
configuration for the compression of cable terminals. Proposed in this
case is a pumping device which has a high-pressure delivery piston and a
low-pressure delivery piston. The low-pressure delivery piston comprises a
spring-mounted pipe section with a pipe bottom which forms the piston
head. The low-pressure delivery piston is displaced counter to the spring
force by a continuation of the high-pressure delivery piston, hydraulic
liquid being sucked in from a supply container. The projection of the
high-pressure delivery piston then moves back and, on account of the
spring acting upon it, the low-pressure delivery piston delivers the
sucked-in hydraulic liquid into the working space. The delivery stops as
soon as the pressure in the delivery chamber can no longer be overcome by
the spring force. In the known pump, then only the high-pressure piston
continues to operate.
Setting out from the above mentioned prior art, the invention deals with
the technical problem of specifying a piston pump for delivering a fluid
at low pressure and at a higher pressure, which permits effective delivery
with a construction which is as simple as possible.
This technical problem is solved initially and substantially in the
subject-matter of Claim 1, the solution being based on the fact that the
fluid delivery path passes through the low-pressure delivery piston, that
a valve is provided in the low-pressure delivery piston, which valve shuts
in the case of movement in the delivery direction, and that the
high-pressure delivery piston operates in the pressure chamber of the
low-pressure delivery piston. There is only one common pressure chamber
for the low-pressure delivery piston and for the high-pressure delivery
piston. The low-pressure delivery piston is inevitably pushed back, namely
by the high-pressure delivery piston. According to the invention, a
simplified design of the piston pump is firstly achieved by the fact that
the low-pressure delivery piston and the high-pressure delivery piston
operate on the same pressure chamber. There is only one pressure chamber
or pump chamber. The losses due to throttling operations are minimized or
are no longer present. Furthermore, the fluid delivery path passes through
the low-pressure delivery piston with a valve which shuts when the
low-pressure delivery piston moves in the delivery direction. This also
means that fluid flows into the pressure chamber when the low-pressure
delivery piston moves counter to the delivery direction, the pressure in
the pressure chamber not being higher than in the inflow direction ahead
of the low-pressure delivery piston. On the contrary, the prevailing
pressure is generally the same as in the inflow direction ahead of the
low-pressure delivery piston, reduced by the force of a spring acting on
the low-pressure delivery piston. When the valve in the low-pressure
delivery piston is open, the pressure is virtually the same on both sides
of the low-pressure delivery piston. The embodiment advantageously has few
individual parts. Apart from the inlet valve and the outlet valve, only
the valve in the low-pressure delivery piston is still required. Moreover,
the constructional shape is simpler. There is only one pressure chamber,
both for the low-pressure stage and the high-pressure stage. Furthermore,
provision is made for the movement of the low-pressure delivery piston to
take place counter to its prestress by the high-pressure delivery piston.
The high-pressure delivery piston can act, in particular, directly on the
surface of the low-pressure delivery piston. The high-pressure delivery
piston preferably has, with regard to the pump, a smaller active
cross-sectional area than the low-pressure delivery piston. The ratio may
be, for example, 4:1 with regard to the area of the low-pressure delivery
piston relative to the area of the high-pressure delivery piston. Good
values are also achieved in practice with ratios of 6 to 7:1. In a further
preferred embodiment, provision is also made for the high-pressure
delivery piston to actuate the valve which is provided in the low-pressure
delivery piston and shuts when the low-pressure delivery piston moves in
the delivery direction. Owing to the fact that the high-pressure delivery
piston does not have to bear against the low-pressure delivery piston when
the low-pressure delivery piston moves in the delivery direction, in
continuation of this concept, a valve which is very simple in
construction, namely a plate valve, may-be provided in the low-pressure
delivery piston. The valve in the low-pressure delivery piston furthermore
preferably has a stem-like projection or an actuating end which passes
through-the piston head of the low-pressure delivery piston. By means of
this actuating end, actuation of the valve can take place by means of the
high-pressure delivery piston in the manner described. The prestress of
the low-pressure delivery piston into its delivery end position is
advantageously achieved by means of a spring, furthermore preferably by
means of a helical spring (compression spring). With regard to the valve
contained in the low-pressure delivery piston, provision may also be made,
in particular, for the spring which acts on the low-pressure delivery
piston to prestress the valve into the closure position. Another preferred
option is that the fluid volume in the piston pump, i.e. on the inlet side
of the low-pressure delivery piston and in the pressure chamber, is as low
as possible. In a variant, provision is made for this by the fact that the
low-pressure delivery piston has a stem-like projection on the back to
reduce the fluid volume between the inlet valve and the low-pressure
delivery piston. In the same manner, a projection on the rear wall in the
cylinder which receives the low-pressure delivery piston may also be
provided, for example, or a combination of these measures. In a further
variant, to achieve a high level of easy maintenance, provision is also
made for the pump cylinder to have a base which can be opened in service.
Owing to the fact that the pump cylinder base can be opened in service, it
is possible, for example, in a simple manner to exchange or service the
spring and/or the low-pressure delivery piston with the valve provided
therein. For this purpose, the pump cylinder base may, in further detail,
be secured by a screw connection in the pump housing. For this purpose, it
is also recommended that the pump cylinder base is configured, as a whole,
in a cup-like manner with a screwing-in thread on an outer wall of the cup
edge. In combination or as an alternative thereto, it is also possible for
the guide of the high-pressure delivery piston and, if appropriate, a part
of the adjoining piston head to be screwed in this manner and to be
exchangeable.
Furthermore, the invention is explained below with reference to the
attached drawing which, however, illustrates only one exemplary
embodiment.
FIG. 1 shows a diagrammatic cross-sectional view of a piston pump;.
FIG. 2 shows, in the illustration a, b and c, the sequence of a delivery
cycle at low pressure;
FIG. 3 shows, in the illustration a, b and c, the sequence of a delivery
cycle at high pressure;
FIG. 4 shows the diagrammatic front view of a piston pump of a second
embodiment;
FIG. 5 shows a diagrammatic cross-sectional view of a motor-driven
hand-held device with a piston pump according to FIG. 4;
FIG. 6 shows an embodiment which is modified compared to FIG. 4; and
FIG. 7 shows a further embodiment in which the actuation takes place by
means of a hand lever.
Initially with reference to FIG. 1, a piston pump 1 for delivering a fluid
at low pressure and at a higher pressure is illustrated and described. The
piston pump 1 may be used in very many different ways. With simple,
manually actuated pumps, the high-pressure delivery piston can be actuated
by a hand lever and, with the motor-driven manual devices already
mentioned above, by a motor, such as an electric motor. The essential
factor is that firstly, without load, a rapid operation is required,
corresponding to a high delivery volume per stroke, and then higher
pressures have to be applied under loading (with a lower delivery volume
per stroke).
The piston pump 1 has a pump cylinder 2 in which a low-pressure delivery
piston 4 can be moved counter to the prestress exerted by a spring 3. The
low-pressure delivery piston 4 furthermore has a passage path 5 for the
hydraulic fluid which is being pumped here. The fluid passage path 5 is
closed by a valve 6 configured as a non-return valve. The valve 6 shuts
when the low-pressure delivery piston 4 moves in the delivery direction,
and can open when the low-pressure delivery piston 4 moves counter to it &
delivery direction.
The low-pressure delivery piston 4 operates on a pressure chamber 7. The
valve 6 correspondingly opens only when the pressure in the pressure
chamber 7 is lower than on the inlet side in an inflow chamber 8 of the
low-pressure delivery piston 4.
Furthermore, the piston pump 1 has an inlet valve 9 and an outlet valve 10.
The inlet valve 9 is arranged in a line connection to a fluid supply
chamber. The outlet valve 10 is arranged in a line connection to a working
space not illustrated in FIG. 1 (cf. also fluid supply chamber 26 and
working space 27 in FIG. 5).
Also operating in the pressure chamber 7 is a high-pressure delivery piston
11 which can basically be driven in different ways which are not
illustrated in detail in FIG. 1; for example, by means of an eccentric
drive connected to an electric motor, by means of a manual drive, or
another kind of drive which generates reciprocating motion. The range of
movement of the high-pressure delivery piston 11 is indicated by the
dashed illustration.
The high-pressure delivery piston 11 has a smaller active cross-section
than the low-pressure delivery piston 4. The ratio here is about 4:1
(low-pressure delivery piston to high-pressure delivery piston).
The functioning of the piston pump 1 is explained in greater detail with
reference to FIGS. 2 and 3. FIG. 2a illustrates the delivery end position
of the low-pressure delivery piston 4 in low-pressure operation, i.e. at
low pressure in the working space. The spring 3 still exerts a prestress
which, in the exemplary embodiment, for example, corresponds to a value of
10 bar. The high-pressure delivery piston 11 is in its position which is
retracted to the furthest extent; in the exemplary embodiment, it
terminates at the end face approximately flush with a (lower) cylinder
wall 12 (of the pressure chamber 7).
FIG. 2b illustrates the fact that the high-pressure delivery piston 11 is
in--end face--contact with the low-pressure delivery piston 4 and is
moving the latter back counter to the effect of the helical spring 3.
While it is moving back, the valve 6 is open. Fluid is flowing from the
inflow chamber 8, at the back in relation to the low-pressure delivery
piston 4, through the fluid delivery path 5 into the pressure chamber 7.
Since the volume of the pump (inflow chamber 8 and pressure chamber 7) is
constantly being reduced at the same time by the retracting high-pressure
delivery piston 11, the outlet valve 10 is also open and fluid is flowing
into the working space.
FIG. 2c illustrates the delivery stroke of the low-pressure delivery piston
4. On account of the effect of the helical spring 3, the low-pressure
delivery piston 4 moves in the direction of its delivery end position
according to FIG. 2a after the high-pressure delivery piston 11 has begun
its retraction movement. In this case, the valve 6 is closed and, on the
inflow side, fluid is sucked into the inflow chamber from the supply
container via the opening inlet valve 9 on account of the resulting
vacuum. At the same time, fluid is displaced from the pressure chamber 7
via the open outlet valve 10 in the working space. It can be seen that the
volume of fluid displaced in the process is dependent on the
cross-sectional ratio of the low-pressure delivery piston 4 to the
high-pressure delivery piston 11. The greater
the--effective--cross-sectional ratio of the two pistons is, the more
fluid is delivered into the working space via the outlet valve 10 in the
low-pressure stage.
Referring to FIGS. 3a to 3c, a corresponding delivery cycle is illustrated,
in which it is assumed that the pressure in the working space is higher
than the prestress of the low-pressure delivery piston 4 in its delivery
end position. The pressure should be substantially higher than the
pressure of about 10 bar as first mentioned. The deciding factor is that
the pressure in the working space is higher than that due to the helical
spring (compression spring 3) in the upper position of maximum prestress
of the low-pressure delivery piston 4.
FIG. 3a illustrates the delivery end position of the high-pressure piston
11. The high-pressure delivery piston 11 is retracted into the pressure
chamber 7 to its maximum extent.
FIG. 3b illustrates a condition in which the high-pressure delivery piston
11 is on the path of its return stroke. The outlet valve 10 is closed,
because the pressure in the pressure chamber 7 is now only determined by
the spring 3. This may be, for example, a pressure of between 10 and 20
bar. This pressure is thus substantially lower than the pressure to be
assumed as high in this state in the working space. The reducing pressure
or the compensation of the volume enlargement resulting due to the
extending high-pressure delivery piston 11 leads to a trailing movement of
the low-pressure delivery piston 4. As a result and at the same time,
fluid is sucked into the inflow 8 from the supply container through the
opening inlet valve 9. During the process, the low-pressure delivery
piston 4 does not reach the delivery end position according to FIG. 2a,
but a position which is ahead of it in the delivery direction until
compensation of the volume proportion of the extending part of the
high-pressure delivery piston 11 has been reached.
FIG. 3c illustrates a point in time during the delivery stroke of the
high-pressure delivery piston 11. The high-pressure delivery piston 11 is
not (yet) in contact with the low-pressure delivery piston 4. As a result
of the nevertheless prevailing pressure increase, the inlet valve 9 is
closed. In contrast, the outlet valve 10 is open, since the pressure in
the pressure chamber 7 has increased on account of the retracted
high-pressure delivery piston 11 to the extent that it exceeds the
pressure in the working space.
A further embodiment of the piston pump 1 is illustrated with reference to
FIG. 4. The position represented corresponds to that of FIG. 3a, although
this position here can relate both to a low-pressure and to a
high-pressure cycle.
The inlet valve 9, the outlet valve 10 and the high-pressure delivery
piston 11 are essentially unchanged.
Here, however, the low-pressure delivery piston 4 has a stem-like
projection 13 at the rear end, this being the case at least in terms of
function.
In fact, the stem-like projection 13 is provided on a plate 14 which is
part of the valve 6 in this case. The valve 6, or in the specific
embodiment the plate 14, furthermore has an actuating projection 15 on its
front side.
The stem-like projection 13 results in a minimum fluid volume in the inflow
chamber 8. This is required in order to achieve specific flow speeds
there; moreover also, in order to achieve the least possible deflection on
account of resilience due to the hydraulic liquid during the
(high-pressure) delivery stroke. In general, however, the essential factor
is that a fluid is used for the pump, which fluid is essentially
incompressible.
Customary--oil-like--hydraulic liquids are appropriate here.
In a further detail, the helical spring 3 is arranged, in the embodiment of
FIG. 4, surrounding the cylinder-like projection 13.
Provided in the piston head 17 of the low-pressure delivery piston 4 are
throughflow openings 18 which, in this embodiment, form the fluid delivery
path 5. As can be seem, opening of the valve 6 is achieved by surface
contact between an end face 19 of the high-pressure delivery piston 11 and
the actuating projection 15 of the valve 6, so that fluid flows into the
pressure chamber 11 from the inflow chamber 8 through the openings 18 in
the piston head 17 of the low-pressure delivery piston 4. The valve 6 of
the embodiment according to FIG. 4 is thus not pressure-actuated, but
under enforced control.
In a further detail, it is a significant factor that, in the embodiment of
FIG. 4, the piston head 31 is configured as a screw-in part. On the side
wall, it has an external thread 33 which interacts with a corresponding
internal thread on the pump housing 32. This permits simple exchange and
provides ease of maintenance.
The fact that both the piston guide for the high-pressure delivery piston
11 and the piston head for the low-pressure delivery piston 4 are
configured for screwing in is illustrated in the embodiment of FIG. 6. It
is preferable for only the piston guide for the high-pressure delivery
piston 11 to be configured to be screwed in.
It is furthermore a significant factor that, in this embodiment, a
throughflow path is formed in the low-pressure delivery piston 4, namely
the cylinder-like projection. It is thus possible, on the one hand, to
continue to keep the volume still provided in the compressed position of
the spring 3 as small as possible but, on the other hand, in particular
also to form such a flow path that relatively high flow speeds are always
assured. It is also essential that the design is configured in such a way
that there are few or no dead spaces.
A manually operated motor-powered tool with a piston pump according to the
embodiment of FIG. 4 explained above is illustrated with reference to FIG.
5.
Arranged in the manually operated motor-powered tool 20 is an electric
motor 21 which has a reducing gear 22. The reducing gear 22 acts via a
shaft 23 on an eccentric 24 which, in turn, acts via a rolling bearing 25
on the high-pressure delivery piston 11.
In the manner explained above, for this purpose fluid is pumped into the
working space 27 from the fluid supply chamber 26 and, as a result, an
operating piston 28 is moved into its operating end position counter to
the effect of a restoring spring 29. The return movement of the operating
piston 28 takes place via the restoring spring 29 if--which is not
illustrated in detail here--a drainage valve in the working space 27 is
open, via which the fluid can then flow back into the supply chamber 26.
The drive of the electric motor 21 is effected in further detail by means
of a battery or an accumulator 30.
In the embodiment of FIG. 7, the high-pressure delivery piston 11 is
actuated directly by means of a hand lever 34. For this purpose, the
high-pressure piston 11 is connected specifically to a coaxially aligned
connection piece 35 which is coupled by means of a hook shape 36 to a
carrier pin 37 of the hand lever 34. The hand lever is mounted on the
housing 39 by means of a rotary pin 38 which is independent thereof.
Otherwise the piston pump 1 in the embodiment of FIG. 7 behaves in the same
manner as the piston pump 1 of the embodiments described above, reference
thus being made thereto.
All the features disclosed are essential to the invention. In the
disclosure of the application, the disclosure content of the
associated/attached priority documents (copy of the preliminary
application) is hereby also included to its full extent, also for the
purpose of including features of these documents in claims of the present
application.
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